1. Field of the Invention
The present invention relates in general to automotive speed control systems and in particular to an electronic circuit for disengaging an electronic speed control system when the rate of change of the automobile engine speed exceeds a predetermined amount.
Automotive speed control systems have been developed wherein a speed sensor supplies signals to an engine throttle actuator which enables a vehicle to be maintained at a constant preselected speed. One serious problem of such automotive cruise control systems is that the engine may overrun if the clutch is depressed (in an automobile utilizing a manual transmission) or if the shift selector is moved to neutral (in an automobile utilizing an automatic transmission) while the speed control system is holding the engine throttle in an open position. One prior solution to this problem was to supply a clutch or shift selector disengagement switch which was positioned to be actuated by actual movement of the transmission mechanism and which provided a signal to disengage the speed control system when the clutch was depressed or the shift selector was moved to neutral. However, since there are a large number of different transmission arrangements for use in the many different types of automobiles in use, such an automotive aftermarket speed control device is undesirable because of its cost and complexity.
2. Description of the Prior Art
U.S. Pat. No. 4,355,607 to Blaney discloses a safety disengagement device for an automotive speed control system. The device includes a circuit which compares a present engine speed signal with a previous engine speed signal furnished after a time delay to produce an output signal when a preselected engine speed differential occurs during the delay period. The output signal is utilized to disengage the speed control system directly or, alternatively, to turn off the engine ignition system.
U.S. Pat. No. 3,828,742 to Weis discloses a control system for monitoring and controlling an engine as a function of engine speed. The control system includes a control device which continuously monitors engine speed sensed through a magnetic pickup means and causes engine shutdown by means of an engine shutdown device when an overspeed condition occurs. In addition, the control device actuates a warning device when an underspeed condition occurs.
Other related speed control devices are disclosed in U.S. Pat. Nos. 3,878,915 to Purland et al. and 4,098,242 to Anderson.